The present invention relates to a golf ball having a superior impact resilience (flying performance) and shot feeling (realize a soft feeling), a golf ball cover material composition capable of obtaining the golf ball having the superior impact resilience and durability and a good appearance, and a method of manufacturing the composition.
There are two types of golf balls: a two piece golf ball in which a core is covered with a cover material; and a multi-layer structure golf ball having three or more layers in which appropriate intermediate layer or layers are placed between the core and the cover.
In a golf ball, a core having a rubber composition is covered by a cover material such as ionomer resin (ionic ethylene copolymer) having superior impact resistance and durability. More particularly, since a two piece golf ball has a longer flight distance and greater durability, it is preferred by most golfers. However, a two piece golf ball is inferior to a thread-wound golf ball in shot feeling and spin performance, because its feeling is harder at the time of a shot.
Golf balls are proposed in the prior art (Japanese Patent Application Laid-open No. 4-109971, No. 5-123422 or the like) which make the shot feeling soft by softening the two piece golf ball like a golf ball that uses a soft core and a soft cover material, or a golf ball in which the hardness of the core is different from that of the cover material or a golf ball in which the thickness of the cover is adjusted and so on. However, although these golf balls are superior in the spin performance and the shot feeling, their flying performance is insufficient.
The impact resilience and shot feeling of the golf ball are also inconsistent with each other, and thus it is desired that a golf ball adapted to appropriately balance these properties is developed. In order to improve the feeling and the spin performance, golf balls have been proposed (Japanese Patent Application Laid-open No. 6-319830) in which the difference in the hardness between the core and the ball is reduced and the hardness of the cover and the thickness of the cover are adjusted. However, although this golf ball is superior in the shot feeling, its impact resilience is insufficient.
On the other hand, in order to make the shot feeling of the golf ball softer, constitution of a golf ball in which the core is covered with the cover material of the ionomer resin and diene rubber has been recently proposed (Japanese Patent Application Laid-open No. 6-79017). However, if the cover material of the ionomer resin and the diene rubber is used, color of the cover changes during or after manufacturing the golf ball, and thus the commercial value of the golf ball is disadvantageously reduced. Furthermore, when the ionomer resin and the diene rubber are kneaded for manufacturing the cover material made of the ionomer resin and the diene rubber, blocking of the diene rubber often occurs before introducing the diene rubber into a screw extruder. When such blocking occurs, it becomes difficult to supply the material of the ionomer resin and the diene rubber to the screw extruder, and, as a result, the productivity is disadvantageously reduced.